This is exactly the difference I experienced when upgraded to the AK from the A4 MkI.
Without using the filter (cutoff fully open) the AK displayed good low end when playing lower notes, whilst the A4mki would roll off as play down the octaves. The filter also seemed to have a fuller rounder tone but maybe that could have been because the source was better (oscillators). The A4mkI sounded thinner. At the time I was using the A4mki for a sound design project (many hours of work) and difference was quite clear.
The MKII has some other changes such as the overdrive so once you start deep diving making patches the differences can become more obvious depending on the patch.